Rotonlike

Rotonlike refers to a feature in the excitation spectrum of a many-body system where the energy as a function of momentum shows a local minimum at a nonzero wavevector, known as a roton minimum. The term echoes the rotons identified in superfluid helium-4, where the dispersion relation has a pronounced minimum at finite momentum. In rotonlike systems, the minimum is qualitatively similar, but the underlying microscopic origin may differ from the original helium scenario.

Rotonlike features appear in a variety of interacting quantum fluids and solids. In ultracold atomic gases, nonlocal interactions such as dipolar forces or engineered long-range interactions can produce a roton minimum in the dispersion. Other platforms, including exciton-polariton condensates and certain density-wave–prone solid-state systems, can display analogous dispersions. The roton idea is typically inferred from measurements of the dynamic structure factor S(k, ω) or from the excitation spectrum E(k), where a pronounced minimum appears at a finite momentum.

The physical significance of a rotonlike dispersion lies in its tendency to signal an approach toward density modulation or crystalline order. Softening of the roton minimum with increasing density or interaction strength can indicate an impending instability toward structured phases, such as density waves or supersolidity, depending on the system. In helium, the phenomenon is tied to strong correlations; in other platforms, rotonlike features serve as a diagnostic of collective behavior and phase transitions.

In usage, rotonlike is a descriptive term denoting a qualitative resemblance to rotons rather than a claim of identical microscopic mechanisms. It denotes a dispersion with a local minimum at finite momentum and a finite energy gap above it.